U.S. patent number 6,890,786 [Application Number 10/131,452] was granted by the patent office on 2005-05-10 for wafer scale processing.
This patent grant is currently assigned to Brillian Corporation. Invention is credited to Douglas J. McKnight, Tobias W. Walker, Kam Wan.
United States Patent |
6,890,786 |
Walker , et al. |
May 10, 2005 |
Wafer scale processing
Abstract
This invention relates to a method of fabricating a light
modulation system having a semiconductor substrate. In one
exemplary method, an optical layer is applied over a semiconductor
substrate which includes a plurality of integrated circuits. Each
of these integrated circuits is capable of creating a separate
display device. A protective layer is then applied over the optical
layer. The plurality of integrated circuits is then singulated.
Various other embodiments of apparatuses and methods are
disclosed.
Inventors: |
Walker; Tobias W. (Louisville,
CO), McKnight; Douglas J. (Boulder, CO), Wan; Kam
(Lafayette, CO) |
Assignee: |
Brillian Corporation (Tempe,
AZ)
|
Family
ID: |
24484049 |
Appl.
No.: |
10/131,452 |
Filed: |
April 22, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
619969 |
Jul 20, 2000 |
6476415 |
Nov 5, 2002 |
|
|
Current U.S.
Class: |
438/48; 257/59;
257/644; 257/650; 257/72; 257/E21.599; 349/153; 349/158; 349/187;
349/190; 349/73; 438/128; 438/149; 438/151; 438/157; 438/283;
438/723 |
Current CPC
Class: |
G02F
1/133351 (20130101); H01L 21/78 (20130101); G02F
1/13363 (20130101); G02F 1/136277 (20130101) |
Current International
Class: |
G02F
1/13 (20060101); G02F 1/1333 (20060101); H01L
021/00 () |
Field of
Search: |
;257/59,72,644,650
;349/73,153,158,187,190 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pham; Hoai
Assistant Examiner: Louie; Wai-Sing
Attorney, Agent or Firm: Baker Botts L.L.P.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a divisional of Application No. 09/619,969, filed Jul. 20,
2000, now U.S. Pat. No. 6,476,415 B1, issued Nov. 5. 2002.
Claims
What is claimed is:
1. A method of fabricating a light modulation system having a
semiconductor substrate, said method comprising: applying a first
glass layer over said semiconductor substrate wherein said first
glass layer has a transparent electrode and a plurality of gaps
between said first glass layer and said semiconductor substrates;
applying an optical element layer over said first glass layer which
includes a plurality of integrated circuits, each of which is
capable of creating a separate display device; applying a second
glass layer over said optical element layer; and singulating said
plurality of integrated circuits.
2. A method as in claim 1, further comprising: introducing a liquid
crystal material into one of said gaps after said singulating.
3. A method as in claim 2 wherein said semiconductor substrate
comprises a mono-crystalline silicon material.
4. A method as in claim 2 further comprising: creating a spacer
layer over said semiconductor substrate, said spacer layer creating
said plurality of gaps.
5. A method as in claim 4 wherein said semiconductor substrate is a
semiconductor wafer that has said plurality of integrated circuits
fabricated into said semiconductor substrate.
6. A method of fabricating a light modulation system having a
semiconductor substrate, said method comprising: applying a first
glass layer over said semiconductor substrate; cutting said first
glass layer prior to applying an optical element layer; applying
said optical element layer over said first glass layer which
includes a plurality of integrated circuits, each of which is
capable of creating a separate display device; applying a second
glass layer over said optical element layer; and singulating said
plurality of integrated circuits.
7. A method as in claim 6 wherein said optical element layer is
applied over said first glass layer by lamination.
8. A method of fabricating a light modulation system having a
semiconductor substrate, said method comprising: applying a first
glass layer over said semiconductor substrate; applying an optical
element layer over said first glass layer which includes a
plurality of integrated circuits, each of which is capable of
creating a separate display device, wherein said optical element
layer comprises an optical retarder layer which is one of a
uniaxial retarder or a biaxial retarder; applying a second class
layer over said optical element layer; and singulating said
plurality of integrated circuits.
9. A method of fabricating a light modulation system having a
semiconductor substrate, said method comprising: applying a first
glass layer over said semiconductor substrate; applying an optical
element layer over said first glass layer which includes a
plurality of integrated circuits, each of which is capable of
creating a separate display device, wherein said optical element
layer comprises an optical retarder layer that comprises a first
retarder element and a second retarder element that are laminated
together; applying a second glass layer over said optical element
layer; and singulating said plurality of integrated circuits.
10. A method of fabricating a light modulation system having a
semiconductor substrate, said method comprising: applying a first
glass layer over said semiconductor substrate; applying an optical
element layer over said first class layer which includes a
plurality of integrated circuits, each of which is capable of
creating a separate display device, wherein said optical element
layer comprises an optical polycarbonate retarder layer; applying a
second class layer over said optical element layer; and singulating
said plurality of integrated circuits.
11. A method of fabricating a light modulation system having a
semiconductor substrate, said method comprising: applying a first
glass layer over said semiconductor substrate; applying a an
optical element layer over said first class layer which includes a
plurality of integrated circuits, each of which is capable of
creating a separate display device, wherein said optical element
layer comprises an optical liquid crystal polymer retarder layer;
applying a second glass layer over said optical element layer; and
singulating said plurality of integrated circuits.
12. A method of fabricating a light modulation system having a
semiconductor substrate, said method comprising: applying a first
glass layer over said semiconductor substrate; applying an optical
element layer over said first glass layer which includes a
plurality of integrated circuits, each of which is capable of
creating a separate display device; applying a second glass layer
over said optical element layer, wherein said optical element layer
is attached to said second glass layer by one of (a) a pressure
sensitive adhesive; (b) a urethane adhesive; or (c) an ultraviolet
cured adhesive; and singulating said plurality of integrated
circuits.
13. A method of fabricating a light modulation system having a
semiconductor substrate, said method comprising: applying a first
glass layer over said semiconductor substrate; applying an optical
element layer over said first glass layer which includes a
plurality of integrated circuits, each of which is capable of
creating a separate display device, wherein said optical element
layer is attached to said first glass layer by one of (a) a
pressure sensitive adhesive; (b) a urethane adhesive; or (c) an
ultraviolet cured adhesive; applying a second glass layer over said
optical element layer; and singulating said plurality of integrated
circuits.
14. A method of fabricating a light modulation system having a
semiconductor substrate, said method comprising: applying a first
glass layer over said semiconductor substrate; applying an optical
element layer over said first glass layer which includes a
plurality of integrated circuits, each of which is cable of
creating a separate display device, wherein said optical element
layer comprises an optical retarder layer; applying a second glass
layer over said optical element layer, wherein said optical element
layer is attached to said second glass layer by an adhesive which
is different than an adhesive which attaches said optical element
layer to said first glass layer; and singulating said plurality of
integrated circuits.
15. A method of fabricating a light modulation system having a
semiconductor substrate, said method comprising: applying a first
class layer over said semiconductor substrate: applying an optical
element layer over said first glass layer which includes a
plurality of integrated circuits, each of which is capable of
creating a separate display device; applying a second glass layer
over said optical element layer: cutting with a first cut said
second glass layer after said first glass layer and said second
glass layer and said optical element layer have been applied over
said semiconductor substrate; cutting with a second cut, after said
first cut, said first glass layer and said optical element layer;
and singulating said plurality of integrated circuits.
16. A method as in claim 15 wherein said first cut has a larger
dimension that said second cut.
17. A method as in claim 16 wherein said larger dimension is a
width, which is related to a width of a blade used to cut.
18. A method of fabricating a light modulation system having a
semiconductor substrate, said method comprising: applying a first
glass layer over said semiconductor substrate; applying an optical
element layer over said first glass layer which includes a
plurality of integrated circuits, each of which is capable of
creating a separate display device; applying a second glass layer
over said optical element layer, wherein said second glass layer
has an optical coating; and singulating said plurality of
integrated circuits.
19. A method as in claim 18 wherein said optical coating is an
anti-reflective coating.
20. A method as in claim 6 wherein said cutting is a partial cut
through said first glass layer.
21. A method as in claim 6 further comprising: cutting said optical
element layer after applying said optical element layer over said
first glass layer and before applying said second glass layer.
22. A method as in claim 21 wherein said cutting of said optical
element layer comprises laser cutting of said optical element
layer.
23. A method as in claim 18 wherein said second glass layer is
applied over said optical element layer before said optical element
layer is applied over said semiconductor substrate.
24. A method of fabricating a light modulation system having a
substrate, said method comprising: applying a first class layer
over said substrate, wherein said first glass layer has a first
plurality of transparent electrodes and a plurality of gaps between
said first glass layer and said substrate; applying an optical
element layer over said first glass layer which includes a
plurality of display drivers, each of which is capable of creating
a separate display device; applying a second glass layer over said
optical element layer; and singulating said plurality of display
drivers.
25. A method as in claim 24 further comprising: introducing a
liquid crystal material into one of said gaps after said
singulating.
26. A method as in claim 25 wherein said substrate comprises a
second plurality of electrodes.
27. A method as in claim 25 further comprising: creating a spacer
layer over said substrate, said spacer layer creating said
plurality of gaps.
28. A method as in claim 27 wherein said substrate comprises an
Indium Tin Oxide (ITO) layer and wherein each display driver
comprises a set of parallel electrodes.
29. A method as in claim 28 further comprising: cutting said first
glass layer prior to applying said optical element layer, said
optical element layer being applied over said first glass
layer.
30. A method as in claim 29 wherein said optical element layer is
applied over said first glass layer by lamination.
31. A method of fabricating a light modulation system having a
substrate, said method comprising: applying a first glass layer
over said substrate: applying an optical element layer over said
first glass substrate which includes a plurality of display
drivers, each of which is capable of creating a separate display
device, wherein said optical element layer comprises an optical
retarder layer which is one of a uniaxial retarder or a biaxial
retarder; applying a second glass layer over said optical element
layer; and singulating said plurality of display drivers.
32. A method of fabricating a light modulation system having a
substrate, said method comprising: applying a first glass layer
over said substrate; applying an optical element layer over said
first glass substrate which includes a plurality of display
drivers, each of which is capable of creating a separate display
device, wherein said optical element layer comprises an optical
retarder layer which comprises a first retarder element and a
second retarder element that are laminated together; applying a
second glass layer over said optical element layer; and singulating
said plurality of display drivers.
33. A method of fabricating a light modulation system having a
substrate, said method comprising: applying a first glass layer
over said substrate; applying an optical element layer over said
first glass substrate which includes a plurality of display
drivers, each of which is capable of creating a separate display
device, wherein said optical element layer comprises an optical
retarder layer which comprises a polycarbonate retarder; applying a
second glass layer over said optical element layer; and singulating
said plurality of display drivers.
34. A method of fabricating a light modulation system having a
substrate, said method comprising: applying a first glass layer
over said substrate; applying an optical element layer over said
first glass substrate which includes a plurality of display
drivers, each of which is capable of creating a separate display
device; applying a second glass layer over said optical element
layer, wherein said optical element layer is attached to said
second glass layer by one of (a) a pressure sensitive adhesive; (b)
a urethane adhesive; or (c) an ultraviolet cured adhesive; and
singulating said plurality of display drivers.
35. A method of fabricating a light modulation system having a
substrate, said method comprising: applying a first glass layer
over said substrate; applying an optical element layer over said
first glass substrate which includes a plurality of display
drivers, each of which is capable of creating a separate display
device, wherein said optical element layer is attached to said
first glass layer by one of (a) a pressure sensitive adhesive; (b)
a urethane adhesive; or (c) an ultraviolet cured adhesive; applying
a second class layer over said optical element layer; and
singulating said plurality of display drivers.
36. A method of fabricating a light modulation system having a
substrate, said method comprises: applying a first glass layer over
said substrate; applying an optical element layer over said first
glass substrate which includes a plurality of display drivers, each
of which is capable of creating a separate display device, wherein
said optical element layer comprises an optical retarder layer
which comprises a liquid crystal polymer retarder; applying a
second glass layer over said optical element layer, wherein said
optical element layer is attached to said second glass layer by an
adhesive which is different than an adhesive which attaches the
optical element layer to said first glass layer; and singulating
said plurality of display drivers.
37. A method of fabricating a light modulation system having a
substrate, said method comprising: applying a first glass layer
over said substrate; applying an optical element layer over said
first glass substrate which includes a plurality of display
drivers, each of which is capable of creating a separate display
device; applying a second class layer over said optical element
layer; cutting with a first cut said second glass layer after said
first glass layer and said second glass layer and said optical
element layer have been applied over said substrate; cutting with a
second cut, after said first cut, said first glass layer and said
optical element layer; and singulating said plurality of display
drivers.
38. A method as in claim 37 wherein said first cut has a larger
dimension that said second cut.
39. A method as in claim 38 wherein said larger dimension is a
width, which is related to a width of a blade used to cut.
40. A method of fabricating a light modulation system having a
substrate, said method comprising: applying a first glass layer
over said substrate; applying an optical element layer over said
first glass substrate which includes a plurality of display
drivers, each of which is capable of creating a separate display
device; applying a second glass layer over said optical element
layer, wherein said second glass layer has an optical coating; and
singulating said plurality of display drivers.
41. A method as in claim 40 wherein said optical coating is an
anti-reflective coating.
42. A method as in claim 29 wherein said cutting is a partial cut
through said first glass layer.
43. A method as in claim 29 further comprising: cutting said
optical element layer after applying said optical element layer
over said first glass layer and before applying said second glass
layer.
44. A method as in claim 43 wherein said cutting of said optical
element layer comprises laser cutting of said optical element
layer.
45. A method as in claim 40 wherein said second glass layer is
applied over said optical element layer before said optical element
layer is applied over said substrate.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates the fabrication of liquid crystal display
light modulation systems on a semiconductor substrate by means of a
wafer-scale process.
2. Background Information
Conventional flat-panel displays use electroluminescent materials
or liquid crystals in conjunction with incident light to produce
high quality images in products such as digital wristwatches,
calculators, panel meters, thermometers, and industrial products.
Liquid crystals are a state of matter that mixes the droplet or
pouring property of a liquid and the long-range order property of a
solid. This combination allows an optical activity having a
magnitude without parallel in either solids or liquids. Further,
when a magnetic or electrical field is applied normal to the liquid
crystal material, the liquid crystal material forms a localized
monocrystal that is polar in character. This localized polarization
of the liquid crystal material affects the travel path of light
incident to the liquid crystal material. By controlling the
electrical field applied across the liquid crystal material, the
travel path of light incident to the liquid crystal material can be
controlled to help produce high quality images.
Modern approaches for developing high quality liquid crystal
displays (LCDs), also referred to as liquid crystal spatial light
modulators (SLMs), utilize an active-matrix approach where
thin-film transistors (TFTs) are operationally co-located with a
matrix of LCD pixels. The active-matrix approach using
TFT-compatible LCDs eliminates cross talk between pixels to allow
finer gray scales. Foe example, see U.S. Pat. No. 5,767,828
entitled Method and Apparatus for Displaying Grey-Scale or Color
Images from Binary Images and invented by an inventor of the below
disclosed invention.
Flat-panel displays employing LCD panels generally include five
different layers: A white light source, a first polarizing filter
that is mounted on one side of a circuit panel on which the TFTs
are assembled in arrays to form pixels, a filter plate containing
at least three primary colors arranged into pixels, and a second
polarizing filter. A volume between the circuit panel and the
filter plate is filled with a liquid crystal material. U.S. Pat.
No. 5,868,951 entitled Electro-Optical Device and Method and
co-invented by an inventor of the below disclosed invention relates
to flat-panel displays.
Nematic liquid crystal material is frequently used in LCDs since
its properties are well understood and it is easy to align. This
material will not rotate polarized light when an electric field is
applied across it between the circuit panel and a ground affixed to
the filter plate. The first polarizing filter generally converts
the incident light into linearly polarized light. When a particular
pixel of the display is turned on, the liquid crystal material
rotates the polarized light being transmitted through the material.
Thus, light passes through the filter plate and is detected by the
second polarizing filter.
Conventional liquid crystal displays such as amorphous TFT and
super-twist nematic (STN) displays employ large external drive
circuitry. However, the amorphous silicon transistors of
conventional liquid crystal displays lack the electron mobility and
leakage current characteristics necessary for micro liquid crystal
displays. Moreover, size and cost restraints for micro liquid
crystal displays generally require the drive circuitry of an
integrated circuit to be integrated into the display along with the
pixel transistors. Because the drive circuitry must be fabricated
on the display substrate, micro displays are generally limited to
high quality transistor technology such as single crystal (x--Si)
and polysilicon (p--Si).
Micro display technologies can roughly be divided into two types:
transmissive and reflective. Transmissive micro displays include
polysilicon TFT displays. Polysilicon TFT displays dominate display
technology in high-end projection systems and are also used as
viewfinder displays in hand-held video cameras. They are usually
based on twisted nematic (TN) construction. See U.S. Pat. No.
5,327,269 entitled Fast Switching 270 Degree Twisted Nematic Liquid
Crystal Device and Eyewear Incorporating the Device and invented by
an inventor of the below described invention.
The aperture ratio of a transmissive micro display is obtained by
dividing the transmissive area by the total pixel area.
High-resolution polysilicon displays such as Super Video Graphics
Array (SVGA) are limited to what is considered larger micro
displays having 0.9-1.8 inch diagonal (22.9-45.7 millimeter
diagonal). This is because the area required by the pixel
transistors and the addressing lines reduces the aperture ratio.
Aperture ratios for polysilicon displays are usually around 50%.
Single crystal silicon transmissive displays are similar to
polysilicon TFT displays but use a transistor lift-off process to
obtain single crystal silicon transistors on a transparent
substrate. These displays are often referred to as Liquid Crystal
on Silicon (LCOS) displays when a liquid crystal is used as the
light modulator in the display.
Reflective micro displays are usually based on single-crystal
silicon integrated circuit substrates with a reflective aluminum
pixel forming a pixel mirror. Because it is reflective, the pixel
mirror can be fabricated over the pixel transistors and addressing
lines. This results in an aperture ratio (reflective
area/absorptive area) that is much larger than polysilicon
displays. Aperture ratios for reflective displays can be greater
than 90%. Because of the large aperture ratio and the high quality
silicon transistors, the resolution of a reflective micro display
can be very high within a viewing area that is quite small.
There are several different liquid crystal technologies currently
used in reflective micro displays. These include ferroelectric
liquid crystal (FLC), polymer disbursed liquid crystal (PDLC), and
nematic liquid crystal. Size and resolution of reflective micro
displays may range from 0.25 inch diagonal (QVGA) to 0.9 inch
diagonal (SXGA) (6.4-22.9 millimeter diagonal). Reflective micro
displays are limited in physical size because as the size increases
the cost increases and yield decreases.
Another aspect of liquid crystal display technology is the
methodology used in their fabrication. One liquid crystal display
invention has as an element an optically transmissive first
substrate that may be positioned to receive light incident from the
light source. The fabrication process of this particular invention
teaches positioning a reflective second substrate adjacent to the
first substrate. The second substrate has as active area that may
include a circuit panel and a perimeter seal area surrounding that
active area. To separate the first substrate from the second
substrate, spacers are configured about the perimeter seal area of
the second substrate. Between the first substrate and the second
substrate is a liquid crystal material. In practice, the process
results in individual integrated circuits, which are then laminated
with a retarder and covered with a protective glass sheet. The
problem with this method is that the retarder often-gets scratched
with a production unit so small.
For further background in this area, see Douglas J. McKnight, et
al., 256.times.256 Liquid-Crystal-on-Silicon Spatial Light
Modulator, 33 Applied Optics No. 14 at 2775-2784 (May 10, 1994);
and Douglas J. McKnight et al., Development of a Spatial Light
Modulator: A Randomly Addressed Liquid-Crystal-Over-Nmos Array, 28
Applied Optics No. 22 (November 1989).
SUMMARY OF THE INVENTION
The invention is a method for fabricating a light modulation system
on a semiconductor substrate containing a plurality of integrated
circuits. The invention is to apply the optical element layer (or a
plurality of layers) at the wafer sandwich level, unlike what has
been done previously, applying the optical element layer onto the
individual integrated circuits. The invention takes the silicon
wafer sandwich and cuts partway through the glass side. The glass
layer has a transparent electrode in it. Once back in the clean
room, the surface is cleaned and the retarder film is laminated on.
The retarder has an adhesive (PSA) only on one side. The PSA
adhesive is also laminated onto a separate piece of thin glass. The
retarder with the PSA layer is laminated onto the sandwich. The
thin glass with the PSA layer is brought together adhering the
glass on top of the retarder. The top glass is cut through, just
barely tickling the retarder. The blades are changed and the
retarder is cut through. The assembly is then turned over after
cutting reference flats after a correct alignment and the silicon
is partway cut through. The displays are snapped apart, yielding
individual integrated circuits that already have the optical
element (retarder) laminated onto them, and are capable of creating
separate display devices.
An alternate embodiment of the invention teaches a method by which
a prefabricated top glass/PSA/retarder/PSA assembly is laminated
onto the silicon wafer sandwich, thereby eliminating the operations
involved in the preparation of the retarder and glass surface.
Although the present invention is described in terms of a preferred
embodiment, it may be used in the fabrication of transmissive
displays, reflective display systems, and emissive displays.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a planar side view of an optically transmissive
substrate and a semiconductor substrate or wafer;
FIG. 2 is a perspective top view of the substrates of FIG. 1;
FIG. 3 is a planar side view of the substrate and wafer after the
subsequent processing step of depositing a conductive coating on an
optically transmissive substrate;
FIG. 4 shows the subsequent processing step of depositing alignment
layers on one surface of the substrate and the wafer;
FIG. 5 schematically illustrates an apparatus for rubbing the
surface of the alignment layers with a velvet cloth; FIG. 5 shows a
cylinder having a velvet cloth on its surface;
FIG. 6 shows exemplary rub directions for opposing alignment layers
of a substrate and a wafer 115;
FIG. 7 schematically illustrates a planar top view of a wafer
including a plurality of micro display areas;
FIG. 8 illustrates one micro display area of the semiconductor
wafer;
FIG. 9 shows a cross section of a-display area taken through line
A--A of FIG. 8;
FIG. 10 shows the wafer after the deposition of crossover
material;
FIG. 11 shows an optically transmissive substrate and a wafer
assembled together in a mechanical press;
FIG. 12 shows that a shim plate is flexible enough to conform to
the presence of foreign particles;
FIG. 13 illustrates the crossover material piercing the alignment
layers;
FIG. 14 illustrates the use of a conformal bag press;
FIG. 15 illustrates how the gap may also be used as an entrance for
liquid crystal display material;
FIG. 16 shows the optically transmissive substrate/wafer assembly
lowered into a liquid crystal material bath;
FIG. 17 shows liquid crystal material forced into the cell gap due
to pressure differential;
FIG. 18 illustrates a compensating or retarder film laminated to
the entire surface of the transmissive substrate;
FIG. 19 shows the street areas between the individual display
devices;
FIG. 20 shows the case where the transmissive substrate is
square;
FIG. 21 illustrates how the semiconductor wafer is diced from the
backside;
FIG. 22 shows the backside of the wafer after the step of partial
cutting of the entire semiconductor wafer;
FIG. 23 shows the assembly after the scribing of the glass material
in an X-direction;
FIG. 24 shows the assembly after the scribing of the glass material
in a Y-direction;
FIG. 25 shows a top view of the assembly with the pattern-side of
wafer facing in the up position;
FIG. 26 shows an embodiment where the perimeter of the transmissive
substrate follows the generally round perimeter of the wafer;
FIG. 27 shows material removed from the wafer to provide X- and
Y-registration;
FIG. 28 shows the separated individual display assemblies 300 from
an X-direction, and
FIG. 29 shows the same assemblies 300 from a Y-direction;
FIG. 30 shows a singulated device put in a vacuum chamber;
FIG. 31 shows liquid crystal material forced into the display area
due to a capillary junction;
FIG. 32 shows a singulated device position with the fill port
facing up within a chamber;
FIG. 33 illustrates the chamber in the pressurized state;
FIG. 34 illustrates a cross-section of an individual display from
an X-direction;
FIG. 35 illustrates a cross-section of an individual display from a
Y-direction;
FIG. 36 shows the micro liquid crystal display ready to be packaged
into a micro liquid crystal display panel;
FIG. 37 shows a single-chip radio manufactured by Lucent
Technologies Inc.;
FIG. 38 illustrates a size comparison between a U.S. penny, a
conventional ceramic filter, and a miniature RF filter; and
FIG. 39 shows a tank circuit having a miniature inductor and
capacitor.
FIG. 40 shows an old method for fabricating a light modulation
system on a semiconductor substrate where the integrated circuits
are singulated from a wafer and then an optical element layer is
applied.
FIG. 41A is an example of a method for fabricating a light
modulation system on a semiconductor substrate by applying the
laminate retarder (optical element) onto the surface of the entire
wafer instead of the individual integrated circuits and applying a
protective layer over the laminate retarder.
FIG. 41B is an alternate embodiment of a method for fabricating a
light modulation system on a semiconductor substrate. An optical
layer(s) (e.g. a retarder) is applied to a protective layer,
creating a combined layer. This combined layer (protected optical
layer) is applied to the surface of the entire wafer.
FIGS. 42a, 42b and 42c show a method used in the fabrication of the
light modulation system on a semiconductor substrate.
FIGS. 43a, 43b, and 43c show an alternate embodiment for the method
shown in FIGS. 42a, 42b, and 42c in which one of the components is
prefabricated and readily available.
FIGS. 44A, 44B, and 44C describe some of the variations that can be
used in the sawing process.
FIG. 45 illustrates the first glass substrate on the silicon
wafer.
FIG. 46 shows the glass substrate on the silicon wafer after it has
been cut (first cut).
FIG. 47 shows the retarder applied over the cut glass, which is
over the silicon wafer.
FIG. 48 shows a top glass/pressure sensitive adhesive (PSA)
assembly.
FIG. 49 illustrates the top glass/PSA assembly and the cut glass
substrate wafer in a vacuum chamber.
FIG. 50 shows the top glass/PSA assembly as it is fused onto the
retarder layer.
FIG. 51 shows cuts into the top glass layer.
FIG. 52 illustrates the cuts made with a saw blade into the
retarder layer.
FIG. 53 shows the partial cuts made into the back of the silicon
layer.
FIG. 54 shows the individual integrated circuits with the retarder
layer after the wafer has been cut.
FIG. 55 illustrates an alternate embodiment of the invention in
which the layer that is fused onto the substrate is a top
glass/PSA/retarder/PSA assembly layer.
FIG. 56 shows the glass substrate onto which the top
glass/PSA/retarder/PSA assembly layer is fused.
FIG. 57 shows a plurality of integrated circuits with multiple gaps
created by spacers. These gaps are later filled with a liquid
crystal material.
FIG. 58 is a detailed description of an alternative adhesive system
that can be used in place of the PSA.
DETAILED DESCRIPTION OF THE INVENTION
In the following description, numerous specific details are set
forth such as specific materials, processing steps, processing
parameters, etc., in order to provide a thorough understanding of
the invention. One skilled in the art will recognize that these
details need not be specifically adhered to practice the claimed
invention. In other instances, well known processing steps,
materials, etc., are not set forth in order not to obscure the
invention. As indicated under MPEP 2164.01, a patent need not
teach, and preferably omits, what is well known in the art.
The following describes an embodiment of forming a liquid crystal
display, cell, or device, in accordance with the invention. FIG. 1
shows a planar side view of optically transmissive substrate 100
and semiconductor substrate or wafer 115. In this embodiment, the
character of substrate 100 is optically transmissive where
optically transmissive substrate 100 may serve as a cover that is
positioned to receive light incident from a light source (not
shown). Moreover, optically transmissive substrate 100 may be
approximately 1.1 millimeters (mm) thick. Optically transmissive
substrate 100 may include cover glass material 102, such as Corning
1737 industrial grade boroaluminosilicate glass available from
Applied Films Corporation of Boulder, Colo. With the processing
temperature ranges for making liquid crystal displays being between
0 degrees Celsius (degs. C.) and 300 degs. C., Corning 1737 is a
preferable glass material because it is readily availability and
its coefficient of thermal expansion (Corning 1737
CTE=37.6.times.10.sup.-7 /deg. C.) is very close to that of
silicon. In this embodiment, optically transmissive substrate 100
may include a film of retarder layer 110 laminated to glass
material 102 as seen in FIG. 1 and FIG. 18. Retarder layer 110
serves to compensate for residual birefringence in liquid crystal
during the "on" (black) state. Retarder layer 110 improves the
contrast of the display.
FIG. 1 also shows semiconductor wafer 115 that contains, for
example, a plurality of flat-panel display circuitry. The circuitry
preferably is based on single-crystal silicon integrated circuit
substrate technology with a reflective pixel layer. In the
embodiment shown, the individual display circuitry of wafer 115 is,
for example, reflection mode circuitry. This reflection is
illustrated in FIG. 1 by reflective pixel layer 125. Reflective
pixel layer 125 is fabricated preferably out of aluminum over the
circuitry having pixel transistors and addressing lines within
backplane 120 of wafer 115. In this embodiment, the aluminum
provides a reflective character to pixel layer 125. Other materials
such as gold or silver that are capable of reflecting sufficient
undiffused light to form a virtual image so as to faithfully
reflect or give a true picture may be used. It is to be appreciated
that the invention is not limited to semiconductor wafer arrays.
Other substrate arrays such as, for example, silicon on insulator
(SOI) arrays, can also be used to form the individual display
devices of the invention.
FIG. 2 is a perspective top view of the substrates of FIG. 1. FIG.
2 shows cover glass 102 situated above circuitry pattern-side 117
of semiconductor wafer 115. Wafer 115 is shown with reflective
pixel layer 125 over a plurality of reflection mode display
circuitry revealed on pattern-side 117 of backplane 120.
FIG. 3 is a planar side view of substrate 100 and wafer 115 after
the subsequent processing step of depositing conductive coating 130
on optically transmissive substrate 100. In one embodiment,
optically transmissive substrate 100 is glass material 102 made of
Corning 1737 glass having conductive coating 130 of
Indium-Tin-Oxide (ITO) applied to one side. ITO is a transparent
metal oxide coating that may be deposited on glass material 102 by
way of a sputtering operation. ITO is an industry standard
conductive film because of its high optical transmission and low
electrical resistance. The ITO may be combined in multiple layers
with other optical films, such as silicon dioxide, to reduce
internal reflections in the liquid crystal display. U.S. Pat. Nos.
5,230,771, 5,171,401, and 5,032,221 were co-invented by an inventor
of this patent and relate to plasma etching of Indium Tin
Oxide.
In this embodiment, conductive coating 130, such as ITO layer, is
not patterned. It has been found that depositing conductive coating
130 without patterning, simplifies the manufacturing process
because it eliminates the need for photolithography processing.
Importantly, un-patterned cover glass substrate 100 also simplifies
the assembly process because it allows for a simple mechanical
alignment of substrate 100 and wafer 115 rather than a more
complicated camera-assisted alignment as is conventionally
employed.
FIG. 4 shows the subsequent processing step of depositing alignment
layers 135 on one surface of optically transmissive substrate 100
and on a complementary surface of semiconductor wafer 115. In one
embodiment, alignment layer 135 is a polyimide material
manufactured by Nissan Chemical Industries of Tokyo, Japan.
Polyimide is an industry standard material for nematic liquid
crystal alignment layers because of its easy of application, its
excellent anchoring of liquid crystal molecules, and its support of
a wide range of pre-tilt angles. In one embodiment, alignment layer
135 is NISSAN SE-7492.TM. polyimide material purchased as a
solution to be spin-coated on substrate 100 and substrate 115. In
this embodiment, the polyimide initially has a 6% solids content.
Prior to deposition onto optically transmissive substrate 100, the
polyimide is diluted with Nissan Solvent 21 (or Nissan Solvent 2M)
to a 2% solid solution. NISSAN SE-7210.TM. may also be used for
alignment layer 135.
In the application of alignment layer 135, optically transmissive
substrate 100 and semiconductor wafer substrate 115 are spun-coated
with a 2% solids polyimide solution. Spin coating is a method of
film deposition that provides a uniform coating across the surface
of the substrate. Spin coating equipment is widely used in the
display processing industries.
After substrate 100 and wafer 115 are coated with alignment layers
135, the polyimides of alignment layers 135 are cured. The
substrates first receive a low temperature soft bake (e.g., 80 deg.
C. on metal surface in convection oven) to remove the solvents,
then a high temperature hard bake (e.g., ramp from 80 deg. C. to
240 deg. C. in 30 minutes; total hard bake cycle time 90 minutes)
to fully cure the polyimide. The cure processes of the invention
preferably are performed in a clean room convection oven.
One purpose of alignment layers 135 is to establish the optical
reference axis of the liquid crystal material. Once alignment
layers 135 are deposited and cured on substrate 100 and wafer 115,
alignment layers 135 may be aligned in accordance with the desired
light rotation of the liquid crystal material molecules that will
form part of the individual display. The alignment direction of the
liquid crystal molecules is obtained by means of rubbing the
exposed surface of alignment layers 135 with a velvet cloth.
FIG. 5 schematically illustrates apparatus 148 for rubbing the
surface of alignment layer 135 with velvet cloth 145. As a soft
fabric, such as silk, rayon, or nylon, velvet is preferred to
impart the alignment direction because of its smooth, dense pile
and a plain underside. FIG. 5 shows a cylinder 142 having velvet
cloth 145 on its surface. Cylinder 142 rotates, in this case, in a
clockwise direction. Substrate 100 or 115 having alignment layer
135 rests on a horizontally moving stage 140 so that alignment
layer 135 of substrate 100 or 115 comes in contact with velvet
cloth 145 of cylinder 142. In one embodiment, cylinder 142 rotates
at a speed of 400 revolutions per minute. Stage 140 moves in a
horizontal direction at a speed of approximately 0.75 inches per
second yielding a table stage motion axis relative to cylinder
rotation axis of 90 degrees and rub depth of 0.007 to 0.020 inches.
A suitable material for cloth 145 may be, for example, the YA-20-R
rayon cloth produced by Yoshikawa Chemical Company of Tokyo,
Japan.
FIG. 6 shows exemplary rub directions for opposing alignment layers
135 of substrate 100 and wafer 115 as imparted via apparatus 148 of
FIG. 5. It is to be appreciated that the depth and direction of the
rub is a function of, for example, the liquid crystal molecules
chosen for the individual display. The above description of the rub
process of alignment layers 135 is presented in detail herein by
way of explanation and not by way of limitation, in accordance with
the description of the particular liquid crystal display described
herein.
Once alignment layers 135 are deposited on substrate 100 and 115
and rub directions are established on alignment layers 135, spacers
are applied to semiconductor wafer 115. As described in connection
with FIG. 7, one purpose of applying spacers is to create cell gap
207 (FIG. 11) for the placement of liquid crystal molecules between
substrate 100 and substrate 115.
Spacers may be dispersed randomly across the entire display
substrate, including the viewing area. In some displays, for
example, the spacers in the viewing area maintain spacing
uniformity because glass substrates overlying display circuitry can
warp.
FIG. 7 schematically illustrates a planar top view of wafer 115
including a plurality of micro display areas 155. In one
embodiment, there are 86 micro display areas 155. FIG. 7 shows a
perimeter seal material 150 containing spacers 152 (FIG. 8)
surrounding the perimeter of each of a plurality of display area
155 as well as surrounding the inside perimeter of wafer 115.
Spacers may also be applied randomly across the entire substrate
using a spray-on method. Perimeter seal material 150 may be a
thermal cure adhesive as discussed below and spacers 152 may be
silica spheres.
Material 150 preferably comprises white silica spheres initially in
a dry state. To form perimeter seal material 150, 0.10 grams of
this dry spacer material is mixed with 20 grams of perimeter seal
material. In this embodiment, perimeter seal material 150 is a
heat-cured adhesive, such as Mitsui Chemicals XN-651. It is to be
appreciated that there are many suitable adhesives including, but
not limited to, heat- and ultraviolet-cured adhesives.
Perimeter seal material 150 containing spacers 152 may be applied
using a syringe having a fluid dispensing system, such as one
manufactured by the Camalot Division of Speedline Technologies. An
automatic dispensing system may consist of a syringe mounted above
wafer substrate 115 having full X- and Y-motion capabilities.
Perimeter seal material 150 including spacers 152 may then be
dispensed from a needle.
Perimeter seal material 150 containing spacers 152 are dispensed in
the perimeter seal areas 165 as shown in FIG. 8. As shown in FIG.
7, a pattern (perimeter seal material 150 encapsulating spacers
152) is also dispensed at the edge of wafer 115 in the "unused"
areas of wafer 115. This additional edge pattern is a support
structure that works to prevent wafer 115 from collapsing at its
edges. Without this support structure around the edge of wafer 115,
wafer 115 cannot adequately support the force required to press
together wafer 115 and optically transmissive substrate 100.
Without sufficient press force, a non-uniform cell gap 207 that is
collapsed at the edge of wafer 115 will be formed. The perimeter
seal around the outer edge of wafer 115 also works as a seal to
prevent water from entering the cell gap during a wafer dicing
process.
The next step in forming a LCD display in accordance with an
embodiment of the invention is the deposition of a crossover
material on each display area 155 of wafer 115. Recall that when a
magnetic or electrical field is applied normal to the liquid
crystal material, the liquid crystal material forms a localized
monocrystal that is polar in character. A cross-over may be thought
of as an adhesive material or epoxy into which conductive material
is disbursed so as to aid in creating an electrical path between
the reflection mode display circuitry that resides below the
reflective pixel layer of the wafer and the conductive coating
layer attached to the glass cover. In other words, crossover
material 170 communicates the cover glass drive voltage from
reflective pixel layer 125 of wafer 115 to conductive coating 130
of substrate 100. Conventionally, the cross-over material is made
of silver particles or gold-coated plastic particles.
To conventionally create this electrical path, alignment layers 135
are first removed or etched away to create a path in reflective
pixel layer 125 and in conductive coating 130. Then, the crossover
material is adhered to this path in reflective pixel layer 125 and
brought into contact with the path in conductive coating 130.
Alternatively, a special mask conventionally is created to mask off
the crossover paths prior to applying the polyimide.
In an embodiment of the invention, crossover material 170
preferably contains particles made of conductive nickel. The nickel
particles surprisingly permit crossover material 170 to break
through the polyimide alignment layers 135 to create the desired
electrical path. Thus, the use of nickel particles eliminates the
need to etch away alignment layers 135 or use a mask prior to
applying alignment layers 135.
To form an embodiment of crossover material 170, nickel particles
having 2.0 micron nominal diameters are first mixed with a solvent,
for example isopropyl alcohol, in a concentration of approximately
1.0 gram of cross-over material to 3 grams of solvent. The
materials are mixed in a container and sealed. The mixture is then
placed in an ultrasonic bath for fifteen minutes to thoroughly mix
the particles in the solvent and to-break up any clumps of
material. The solvent is then evaporated and nickel particles are
then mixed with 32 grams of perimeter seal material. Similar to
perimeter seal material 150, a Camalot fluid dispensing machine may
be used to dispense cross-over material 170. In one embodiment, the
machine includes a dispensing needle size of approximately 0.006
inches inside diameter, a needle height of 0.002 inches, and a
dispensing pressure of 28 pounds per square inch.
Once cross-over material 170 is placed on the individual display
area 155 of wafer 115, wafer 115 and optically transmissive
substrate 100 are assembled together. In one embodiment, wafer 115
is placed on a metal surface in a pre-heated convection oven and
baked at 85 deg. C. for approximately 30 minutes as a pre-cure.
This pre-cure bake evaporates solvents in perimeter seal material
150. Wafer 115 is then placed on a vacuum chuck. Then, optically
transmissive substrate 100 is placed over wafer 115 and tacked onto
wafer 115.
FIG. 8 illustrates one micro display area 155 of semiconductor
wafer.115. Display area 155 may include a viewing area 160 and a
perimeter seal area 165. Perimeter seal area 165 includes a
plurality of spacers 152 in perimeter seal adhesive 150. FIG. 8
shows that the spacers 152 and perimeter seal adhesive 150 are
disbursed generally throughout perimeter seal area 165. One
exception is fill port area 167 of perimeter seal area 165. Area
167 is left free of perimeter seal material 150 and spacers 152 to
allow a path for the placement of liquid crystal display material
(material 220, FIG. 16; material 310, FIG. 30; and material 311,
FIG. 32) into display area 160. As shown in FIG. 10, the matrix of
spacers 152 may include more than one spacer 152 across area
165.
Spacers 152 such as shown in FIG. 8 are added to perimeter seal
area 165 to create cell gap 207 (FIG. 11) between wafer 115 and
optically transmissive substrate 100. Cell gap 207 is created to
permit placement of liquid crystal material between wafer 115 and
optically transmissive substrate 100. Perimeter seal material 150
seals the gap between wafer 115 and substrate 100 along the pattern
of perimeter seal area 165 to capture liquid crystal material
within each viewing area 160. Similar to fill port area 167 of FIG.
8, gap 153 of FIG. 7 is left free of perimeter seal material 150
and spacers 152. This permits trapped air to escape as wafer 115 is
affixed to optically transmissive substrate 100. Gap 153 may also
be used as an entrance for liquid crystal display material 220
(FIG. 15).
FIG. 9 shows a cross section of display area 155 taken through line
A--A of FIG. 8. FIG. 9 shows display area 155, display area 160,
perimeter seal area 165, cross-over material 170, and spacers 152.
The outside diameter of spacers 152 is a function of the desired
thickness of the liquid crystal material layer, such as cell gap
207 of FIG. 11. In one embodiment, spacers 152 may be 2.1 micron
silica spheres from Bangs Laboratories of Fishers, Indiana. Spacers
having an outside diameter ranging from 1.5-3.0 microns are used in
this embodiment. Spacers 152 are mixed with perimeter seal material
where the mixture is applied to perimeter seal area 165 of display
area 155 of wafer 115 and to the inside perimeter of wafer 115
(FIG. 7) during a perimeter seal application process.
As noted above, gap 153 of FIG. 7 is left in the wafer perimeter
seal to allow air to escape during a subsequent press and cure
process. Gap 153 also permits the positioning of liquid crystal
material between wafer 115 and optically transmissive substrate 100
prior to dicing or "singulating" wafer substrate 115. Gap 153 is
later filled with an adhesive to complete display area 160.
FIG. 10 shows wafer 115 after the deposition of cross-over material
170. Cross-over material 170 provides, in one manner, electrical
contact between wafer 115 and optically transmissive substrate 100,
such as seen in FIG. 34 and FIG. 35. In the embodiment where
spacers 152 have an outside diameter of 2.1 microns, cross-over
material 170 preferably contains 2.0 micron nominal diameter nickel
particles purchased from Goodfellow, Inc. of Cambridge, England.
Other conductive particles are acceptable substitutes for nickel
where supplied in a particle form having similar conductive
characteristics and break-through characteristics as nickel. In
this embodiment, because conductive coating 130 of transmissive
substrate 100 has no patterning, a mechanical alignment method can
be used during assembly as shown in FIG. 10.
Once optically transmissive substrate 100 and wafer 115 are
assembled together, the substrates may be placed in mechanical
press 180 as shown in FIG. 11. Mechanical press 180 consists of two
heated aluminum plates 185 and 187 hinged together in a clamshell
fashion wherein each shell is parallel to one another. In this
embodiment, bottom plate 187 includes an inflatable bladder 195.
Inflatable bladder 195 provides the direct pressure required to
assemble together transmissive substrate 100 and wafer 115.
Wafer 115 and substrate 100 are pressed together in such a manner
that cross-over material 170 pierces each alignment layer 135 to
make contact between conductive coating 130 and reflective pixel
layer 125 as seen in FIG. 13. In one embodiment, wafer 115 and
substrate 100 are pressed together so that they are separated by a
distance of approximately 2 microns at cell gap 207.
A preferred alternate embodiment to the press assembly technique of
FIG. 11 and FIG. 12 will now be described. FIG. 14 illustrates the
use of conformal bag press 201. Once optically transmissive
substrate 100 and wafer 115 are assembled together as shown in FIG.
10, the assembly may be placed in conformal bag 203 of bag press
201 as shown in FIG. 14. Conformal bag 203 may be a rectangular
shaped, high temperature nylon bag. At this point, tube 206
extending from vacuum pump 204 is coupled to bag end 209 of
conformal bag 203. Vacuum pump 204 may be a food industry,
commercial quality sealer.
With vacuum pump 204 activated, air is drawn from the inside of
conformal bag 203. As air is drawn from the inside of conformal bag
203, conformal bag 203 closes about substrate 100 and wafer 115.
The compression forces of conformal bag 203 are applied equally
about each surface of substrate 100 and wafer 115. Since the force
per unit surface area is greatest on the large, exposed surfaces of
glass layer and back plane 120, glass layer and back plane 120 move
vertically towards one another substantially while maintaining
their original, complementary alignment. As the nickel particles
within cross-over material 170 are urged into alignment layers 135,
the polyimide material of alignment layers 135 separates until
cross-over material 170 contacts reflective pixel layer 125 and
conductive coating 130. This vacuum bag method is preferred to the
clam shell method because, for example, conformal bag 203 easily
adjusts to particles trapped between conformal bag 203 and the
assembly of substrate 100 and wafer 115.
With a vacuum drawn into sealed, conformal bag 203, conformal bag
203 along with the assembly of substrate 100 and wafer 115 is
placed into an oven to cure the adhesive of perimeter seal material
150 and cross-over material 170. Preferably, they remain in the
oven at 175 deg. C. for 60 minutes. In an alternate embodiment, the
air within conformal bag 203 is evacuated and conformal bag 203 is
back filled with another gas, such as nitrogen, helium, or argon,
to displace any oxygen. This back filled gas is then evacuated by
vacuum pump 204 to compress substrate 100 and wafer 115
together.
With the adhesives cured and cross-over material 170 in a position
to communicate the cover glass drive voltage from reflective pixel
layer 125 of wafer 115 to conductive coating 130 of substrate 100,
the cell gaps between the individual display area 155 of wafer 115
and optically transmissive substrate 100 may be filled with liquid
crystal material before individual display devices 300 (FIG. 28 and
FIG. 29) are cut and separated. This filling process is shown in
FIG. 16 and FIG. 17. The assembly (optically transmissive substrate
100 and wafer 115) may be filled by a vacuum fill method common to
filling nematic liquid crystal displays. The entire assembly is put
in a vacuum chamber 210. Chamber 210 is evacuated until the
pressure reaches approximately 10.sup.-1 Torr. In connection with
FIGS. 7-9, a perimeter seal application process was described for
placing perimeter seal material 150 including spacers 152 around
wafer 115. As stated, a perimeter seal adhesive 150 is applied
around the entire wafer 115 except for evacuation gap port 153 to
allow air to escape during the press process. Gap 153 now may be
used to allow the entrance of liquid crystal material in the cell
gap between the assemblies.
As shown in FIG. 16, the optically transmissive substrate/wafer
assembly is lowered into bath 215 containing liquid crystal
material 220. The assembly is lowered into the bath 215 until
evacuation port 153 contacts liquid crystal bath 215. Chamber 210
is then pressurized to atmospheric pressure with a gas, such as
nitrogen, helium, or argon, but preferably air. As illustrated by
way of example in FIG. 8, each of individual display area 155 has a
fill port 167 to allow liquid crystal material to be placed in
display area 160 of individual display device 300. The pressure
difference between cell gaps 207 of the individual display devices
and the ambient, forces liquid crystal material 220 into cell gaps
207 throughout the assembly as illustrate in FIG. 17. Once liquid
crystal material 220 is placed in cell gap 207 of each individual
display device 200, the excess liquid crystal material 220 is
cleaned off evacuation port area 153. An ultraviolet cure adhesive
then is applied to evacuation port 153 and cured with ultraviolet
light to seal the assembly.
FIGS. 16 and 17 illustrate a process where liquid crystal material
is added to the assembly prior to separating the assembly into
individual display devices 300. The liquid crystal material fill
process can also be accomplished once the individual displays are
separated from the assembly. This is discussed in connection with
FIGS. 30 to 33. In this case, evacuation port 153 is filled with an
ultraviolet cured adhesive and cured following just after the press
process.
To produce high quality static as well as dynamic real time color
field images on an active pixel matrix, the nematic liquid crystal
material 220 used in a preferred embodiment should meet several
factors. Color field sequential operation requires a fast pixel
switching time under low voltage operations. Switching speed is
proportional to the square of the cell gap. In order to meet the
fast switching time required for color field sequential operations,
cell gap 207 should be on the order of two microns. This relative
thinness is a factor in selecting the proper viscosity for liquid
crystal material 220. As another factor, the liquid crystal cell
should be capable of rotating the polarization of reflected light
by 90 degrees to obtain bright, high contrast operations. Thus, the
liquid crystal layer performs as a quarter-wave plate in a
preferred embodiment.
The viscosity of liquid crystal material 220 should be as low as
possible to achieve fast switching speeds. Moreover, in respect to
the above factors, the birefringence (delta n or .DELTA.n) of the
liquid crystal material should be approximately 0.1. To achieve low
voltage operations, the threshold voltage of liquid crystal
material 220 should be low, such as a dielectric constant
anisotropy (delta .epsilon. or .DELTA..epsilon.) on the order of at
least 10. In addition, to avoid undesirable temperature effects at
the upper operating range of the micro LCD, the clearing point of
liquid crystal material 220 should be at least 20 deg. C. above the
highest operating temperatures for the micro LCD. One having
ordinary skill in the art of manufacturing liquid crystal material
is able to compose a material meeting the above factors for liquid
crystal material 220.
After the wafer assembly is pressed and sealed, the exterior
surface of optically transmissive substrate 100 is cleaned, for
example, with a solvent. If not already applied, an optical film
then may be applied to the entire surface of transmissive substrate
100. In one embodiment, compensating or retarder film 110 is
laminated to the entire surface of transmissive substrate 100 using
a roller-type lamination machine. The lamination is shown in FIG.
18. Compensating or retarder film 110 is used, in one sense, to
compensate for unwanted birefringence in a display. The film is
used to compensate for residual birefringance in the black state
that results in a darker black. Compensating or retarder film thus
provides an improved contrast between black and white.
Compensating or retarder film 110 must cover the active area of the
display after it is completely assembled. In most display
applications that use a compensating or retarder film, the
compensating or retarder film is laminated to the individual
displays after they are separated from the wafer substrate. This is
a labor-intensive process for small displays with many displays on
a large substrate. The invention teaches a process in which a film,
either retarder or polarizer, is laminated to the glass prior to
separating the displays. It is to be appreciated that compensating
or retarder film 110 can be laminated to each individual display
assembly after they are formed and separated.
In street areas 230 between the individual display devices,
compensating or retarder film 110 is then removed, using a laser as
shown in FIG. 19. This removal exposes transmissive glass material
102 to allow it to be scribed, for example, using a carbide
wheel.
Next, as shown in FIG. 20, in the case where transmissive substrate
100 is square, a dicing saw may be used to scribe relative fiducial
or alignment marks 240 and 245 on optically transmissive glass
substrate 100. To scribe marks 240 and 245, the assembly is placed
on the vacuum chuck of a dicing saw with patterned-side 117 (see
FIG. 2) of semiconductor wafer 115 set in the face up position.
When the assembly is mounted on the vacuum chuck to cut wafer 115
(i.e., circuitry patterned side 117 of wafer 115 is face down)
scribe marks 240 and 245 in transmissive substrate 100 are visible
through glass material 102 and may be used for alignment. The
camera uses alignment or registration marks 240 and 245 to cut
wafer 115 from the backside, since marks 240 and 245 are relative
to micro display area 155 of wafer 115.
Next, as shown in FIG. 21, semiconductor wafer 115 is diced from
the backside, which has no patterns visible on wafer 115 to use as
registration marks for the dicing process. FIG. 21 shows the
assembly placed with optically transmissive substrate 100 face down
(i.e., circuitry patterned side 117 of wafer 115 is "down") on the
vacuum chuck. Scribed alignment marks 240 and 245 on transmissive
substrate 100 are visible through glass material 102 to aid
alignment. The backside of wafer 115 is then cut according to the
patterning registered by the camera and aligned by registration
marks 240 and 245. FIG. 21 shows cut 255 in an X-direction and cut
260 in a Y-direction. FIG. 22 shows the backside of wafer 115 after
the subsequent step of partial cutting of all of semiconductor
wafer 115 in an aligned relation to the patterning on the patterned
side of wafer 115, using registration marks 240 and 245 as an aid,
so that the assembly may be divided or "singulated" into individual
display 300. Wafer 115 is partially cut using a water-cooled wafer
dicing saw. The depth of the saw blade is set to cut partially
through the thickness of wafer 115, in one embodiment, removing
enough material to easily divide wafer 115 in a later process, but
retaining enough material to prevent water from entering cell gap
207 (FIG. 11) between wafer 115 and transmissive substrate 100.
Wafer 115 is then cut in a wet-sawing process. After the partial
cutting, wafer 115 is thoroughly dried.
Optically transmissive glass substrate 100 provides support for
semiconductor wafer 115 during the cutting, drying, and handling
processes. In addition, optically transmissive substrate 100
prevents wafer 115 from flexing and possibly breaking at the cuts,
which would allow water to enter the gap between the substrates.
Because of the support provided by transmissive substrate 100, the
depth of the saw cut can be very close to the thickness of wafer
115 without significant risk of water leakage, for example,
approximately 80% of the thickness of wafer 115 can be cut.
Because no patterns are visible on the backside of semiconductor
wafer 115, an alternative process to the process described above
with reference to FIGS. 21 and 22 is to mount the programmable
camera beneath the dicing saw. Thus, wafer 115 is placed on the
vacuum chuck and aligned to a camera mounted under the vacuum
chuck. A marking device with X-Y motion capabilities, such as a
laser or carbide needle, contacts the backside of wafer 115 and
creates two registration marks on the patterned surface of wafer
115. The registration marks are then used in the cutting
process.
After the cutting process and the assembly drying process, a dry
cutting process is used to scribe transmissive substrate 100. In
the embodiment where optically transmissive substrate 100 is glass
material 102, the glass must be scribed using a dry process
because, after it is scribed, the assembly has no support to
prevent the glass or wafer 115 from cracking. Cracks in either
substrate would allow any liquid used in the process to enter cell
gap 207 between the substrates, i.e., cell gap 207 where liquid
crystal material exists or is to be placed.
To scribe optically transmissive substrate 100 in the embodiment
where material 102 is a glass substrate, the assembly is placed
with pattern-side 117 of wafer 115 facing in the up direction
(optically transmissive substrate 100 side "up") on the vacuum
chuck of a carbide wheel type glass scribing machine such as that
manufactured by Villa Precision International. The glass is scribed
with the carbide scribe wheel in the locations where the glass will
separate, e.g., directly aligned or in an aligned relation with the
scribe areas of wafer 115. The glass can also be cut with a laser
process. FIG. 23 shows the assembly after the scribing of glass
material 102 in an X-direction. Scribing 248 is located in those
areas where optically transmissive substrate will separate. In an
X-direction, in this embodiment, scribing 248 is in an aligned
relation to scribe areas 265 of wafer 115.
FIG. 24 shows the assembly after the scribing of glass material 102
in a Y-direction. In a Y-direction, glass material 102 is not
scribed directly over scribe areas of wafer 115. Instead, scribing
250 is slightly offset. The offsetting serves to expose a portion
of wafer 115 as offset portion 119 for each eventual display. The
exposure of offset portion 119 of wafer 115 is done to allow a
subsequent step of making an electrical connection to the
individual display when the display is packaged. Offset portion 119
is best seen in FIG. 35 and FIG. 36. Exposed area 119 of the
individual display may have bond pads 405 or other contacts coupled
to the circuit devices of the individual display as seen in FIG.
36.
FIG. 25 shows a top view of the assembly with pattern-side 117 of
wafer 115 facing in the up position (optically transmissive
substrate 100 side "up"). FIG. 25 shows transmissive substrate 100
scribed in areas where transmissive substrate is to be separated,
i.e., scribing 248 in an X-direction directly aligned with or in an
aligned relation with the scribe areas of wafer 115 and scribing
250 in a Y-direction offset from the corresponding Y-axis scribe
areas of wafer 115.
After transmissive substrate 100 is scribed, scribe marks 248 and
250 are "vented." Venting is the process by which optically
transmissive substrate 100, such as a glass, is cracked at the
location of the scribe so as to directionally propagate the crack
through the thickness of glass substrate 100. The venting can be
accomplished either manually or using an automated machine
process.
A singulation process embodiment preferred over the square glass
singulation process described in connection with FIGS. 18 through
FIG. 25 will now be described. FIG. 26 shows an embodiment where
the perimeter of transmissive substrate 100 follows the generally
round perimeter of wafer 115. Since the perimeter of transmissive
substrate 100 follows the round perimeter of wafer 115, the same
equipment used to handle wafer 115 may be used to handle substrate
100.
As shown in FIG. 26, wafer 115 with round glass substrate 100 is
mounted to a vacuum chuck with pattern-side 117 of wafer 115 facing
in the up direction. Material is removed from substrate 100 in the
X-direction to reveal top exposed wafer 270 and X-surface substrate
272 and in the Y-direction to reveal side exposed wafer 274 and
Y-surface substrate 276 as shown. As shown in FIG. 27, at top
exposed wafer 270, material is removed from wafer 115 parallel to
X-surface substrate 272 to form X-registration 278. At side-exposed
wafer 274, material is removed from wafer 115 parallel to Y-surface
substrate 276 to form Y-registration 280.
With X-registration 278 and Y-registration 280 machined into wafer
115, wafer 115 is flipped over so that pattern-side 117 is facing
down. Now, cuts similar to those shown in FIG. 21 and FIG. 22 may
be made into backplane 120 using the relative registration provided
by X-registration 278 and Y-registration 280. Transmissive
substrate 100 may now be scribed and vented as discussed in
connection with FIGS. 23, 24, and 25.
This round glass method is preferred since it eliminates the extra
handling tools needed to handle a square piece of glass. This is
especially acute when the diameter of wafer 115 is 8.0 inches.
There, the diagonal of a square piece of glass exceeds 11.3
inches--a length in which most existing equipment in this area is
not capable of handling.
Once transmissive substrate 100 is vented, the remaining silicon
material at the scribe locations unifying wafer 115 can be easily
broken and the individual display assemblies separated as shown in
FIGS. 28 and 29. FIG. 28 shows the separated individual display
assemblies 300 from an X-direction and FIG. 29 shows the same
assemblies 300 from a Y-direction.
An alternative to the above assembly, cutting, scribing, and
venting process is to divide the substrates individually. For
example, wafer 115 can be cut into individual device, then
assembled to an individual transmissive substrate panel of
substrate 100. In this manner, the scribe marks on wafer 115 can be
used to cut wafer 115 into the individual display device from the
top (i.e., circuitry patterned-side 117 facing up). Optically
transmissive substrate 100 components can then be properly aligned
and coupled to wafer 115 in a process similar to that described
above with coupling substrate 100 to wafer 115. A third alternative
is to assemble a similarly sized transmissive substrate 100 to
wafer 115 prior to dividing the assembly into individual display
devices 300. In this embodiment, concerns over cutting wafer 115
from the non-patterned side are addressed by mounting the camera
below the dicing saw to align the cuts to the scribe marks on the
patterned side of wafer 115.
Once the individual display devices 300 are separated from the
wafer, they are either filled with liquid crystal material or, if
already filled, sealed at their fill ports to retain liquid crystal
material 220 in cell gap 207. Recall that in FIG. 8 and, the
accompanying text, perimeter seal material 150 surrounded the wafer
to define each individual display device or assembly and fill port
167 was left to allow the placement of liquid crystal material 220
in display area 160. Where liquid crystal material 220 is located
in cell gap 207 of display area 160 of device 300, fill port 167 is
filled by the application of an ultraviolet cure adhesive that is
cured with an ultraviolet light.
FIGS. 30 and 31 illustrate the situation where the individual
display devices 300 have not been previously filled with liquid
crystal material 220. In FIG. 30, singulated device 300 is put in
vacuum chamber 315. Chamber 315 then is evacuated until the
pressure reaches 10.sup.-1 Torr. Display device 300 is lowered so
that the end of device 300 having fill port 307 contacts liquid
crystal material 310 in bath 305. Fill port 307 may be of fill port
167 shown in FIG. 8. Chamber 315 is pressurized with air to
atmospheric pressure and the pressure difference between cell gap
207 (FIG. 11) and the ambient pressure forces liquid crystal
material 310 into display area 160 as shown in FIG. 31. Once the
individual display device 300 is filled with liquid crystal
material 310, the excess liquid crystal is cleaned off fill port
area 307 and an ultraviolet cure adhesive is applied to fill port
307. The adhesive is then cured with ultraviolet light to seal
display area 160 of display device 300.
An singulated fill embodiment preferred to that described in
connection with FIG. 32 and FIG. 33 will now be described. FIG. 32
shows singulated device 300 position with fill port 307 facing up
within chamber 315. First, air is vacuumed from chamber 315. Then,
a drop of liquid crystal material 310 is placed over fill port 307
by dropper 301. Dropper 301 is preferably in the shape of a short,
sturdy, little teapot having a spout and a handle. With perimeter
seal area generally spanning one-half inches and fill port 207
generally spanning two microns, surface tension holds liquid
crystal material drop 311 in place.
With drop 311 in place, chamber 315 is pressurized. FIG. 33
illustrates chamber 315 in the pressurized state. As chamber 315 is
pressurized, the pressure within viewing area 160 is less than the
pressure in the remaining area of chamber 315. Due to this pressure
difference, liquid crystal material drop 311 is forced into viewing
area 160 as assisted by gravity. Excessive liquid crystal material
311 is cleaned off. Fill port 307 is then plugged with ultraviolet
cure adhesive and this adhesive is then cured with an ultraviolet
light.
FIG. 34 illustrates a cross-section of individual display 300 from
an X-direction, whereas FIG. 35 shows the same assembly from a
Y-direction. FIGS. 34 and 35 show liquid crystal material 310
positioned in cell gap 207 between optically transmissive substrate
100 and wafer 115.
FIG. 36 shows micro liquid crystal display 400 in a state where
micro liquid crystal display 400 is ready to be packaged into a
micro liquid crystal display panel. First, overhang 330 of
substrate 100 shown in FIG. 35 is removed by, for example, applying
a scribe or laser to the glass overhang of display 300. Then, the
material comprising alignment layer 135 disposed in offset portion
119 is removed to expose land pads 405 and other electrical
components located in that area. Alternatively, this area may have
been masked or alignment layer 135 may be retained only to be
pierced using a push through technique. Land pads are electrical
contact pads that permit electrical communication between the
circuitry within micro liquid crystal display 400 and devices
external to micro liquid crystal display 400 such as a device
driver located on a driver board. Micro liquid crystal display 400
may then be enclosed within an anti-static bag and packaged for
shipment with other displays 400 in a box or some other convenient
shipping container.
FIG. 40 shows a method 600, which had been previously used in the
fabrication of a light modulation system. Typically, the integrated
circuits are at least partially tested to ensure their proper
functioning in operation 605 prior to singulation in operation 635.
Operation 610 creates the sandwich as initially consisting of a
glass substrate glued to a silicon wafer, with a thin air gap
between the substrates. In operation 615, the sandwich is sealed
around the outside to prevent water from entering the gap. Water is
used as a coolant in the cutting-process that follows operation
615. In operation 620, a wafer-dicing saw is used to cut partway
through the silicon. The glass side is then scribed in operation
625. The cut on the silicon and the scribe on the glass side are
offset so that when the displays are snapped apart, the bonding
pads on the silicon are exposed and a corresponding overhang of
glass is left on the other side. In operation 630, the displays are
snapped apart, leaving individual integrated circuits. In operation
635, the retarders are laminated onto the individual integrated
circuits. This process is very labor intensive, which gives rise to
the need for a process on the wafer scale. There is also a need for
a glass cover, which is used to protect the retarder because it is
easily damaged and often gets scratched on such a small-scale
process.
FIG. 41A illustrates a flow chart of the generic method of one
embodiment of the invention. A light modulating system is
fabricated using this method. In operation 720, an optical layer or
a plurality of optical-layers (e.g. a retarder) is applied over a
substrate that includes a plurality of integrated circuits, each of
which is capable of creating a separate display device. In
operation 740, a protective layer is applied over the optical
layer(s) (e.g. the retarder). In operation 760, the plurality of
circuits on the substrate is singulated.
FIG. 41B is a flow chart illustrating an alternate embodiment of
the generic method of the invention. A light modulating system is
also fabricated using this method. A combined layer is created in
operation 721 by applying an optical layer(s) to a protective
layer. The combined layers are then applied to a substrate
containing a plurality of integrated circuits in operation 741. In
operation 761, the plurality of integrated circuits is singulated
to create individual displays.
FIGS. 42a, 42b, and 42c show an exemplary method 800 in a flow
diagram, which describes the lamination of an optical element or
retarder on a wafer-scale level. In operation 802, the integrated
circuits (ICs), while still a part of-the wafer, are at least
partially tested to ensure that they function properly. Each of
these ICs, after singulation are used to create a LCOS display,
such as the LCOS display described in U.S. Pat. No. 6,078,303 which
is hereby incorporated herein by reference. This testing is
optional and may be performed after final assembly. Operation 804
creates a sandwich, which consists of a first glass substrate glued
to a silicon wafer, with a thin air gap between the substrates. The
first glass substrate here in one embodiment is Corning 1737F, with
a 150 mm diameter and is 0.7-1.1 mm thick. A spacer layer is
created on the circuit side of the semiconductor wafer and then the
first glass substrate is applied over the spacer layer. Typically,
the spacer layer is attached to the wafer and the first glass
substrate is attached to the spacer layer. The spacer layer may be,
a conventional raised border, which surrounds each integrated
circuit's display array and will create a gap into which a nematic
liquid crystal is inserted. The first glass substrate may be a
conventional cover glass which includes an Indium Tin Oxide (ITO)
transparent electrode layer and an alignment layer (for aligning
the liquid crystal molecules) on the bottom side (facing the wafer)
of the first glass substrate. FIG. 45 shows a cross-sectional view
of the first glass substrate 1002 attached to a semiconductor wafer
1004 without showing the spacer layer which separates the bottom
surface of the first glass substrate from the upper (circuit side)
surface of the semiconductor wafer 1004. FIG. 46 shows the location
of the ITO side of the first glass substrate relative to the
silicon wafer. In operation 806, the sandwich is sealed around the
perimeter of the wafer to prevent water from entering the air gaps.
In operation 808, the first glass substrate is sawed partway
through, to a depth of 0.350 mm. The partial cut allows the glass
to be separated at a later step, but prevents water from entering
the air gap. This is done using a K & S 984-10 Dicing Saw. A 10
mil resin blade made of diamond particles is used at a speed of 6
mm/sec. This blade is usually used to cut hard substances such as
glass. FIG. 46 illustrates the first glass substrate 1002 attached
on the silicon wafer 1004 after it has been cut. In operation 810
the top of the first glass surface is cleaned and in operation 812,
it is spin-dried. After operation 812, the sandwich is aligned
relative to the retarder film. An example of a method for aligning
this retarder film is described in U.S. patent application Ser. No.
09/564,473 filed May 3, 2000 by Douglas McKnight and this
application is incorporated herein by reference. After alignment
with the sandwich in operation 814, the retarder film is laminated
onto the top glass surface of the first glass substrate by means of
a pressure sensitive adhesive (PSA). A 45 nm retarder film with
PSA, available from Polatechno, is used in one embodiment. The
exposed (top) side of the optical element (e.g. retarder) is
covered with a protective film. FIG. 47 illustrates an example of
the optical element layer(s) (e.g. a retarder layer or multiple
retarder layers, polarizer film, or a combination of retarder and
polarizer film) 1008 after it has been attached to the cut first
glass substrate. In operation 816, a separate glass substrate (a
second glass substrate) is cleaned using an Ultratech 602
high-pressure de-ionized water cleaning system. The second glass
substrate is a similar shape to the first glass substrate and may
also be Corning 1737F with a thickness of 0.3 to 0.5 mm. The second
glass substrate is laminated with a pressure sensitive adhesive in
operation 818. The PSA is a conventional 3M PSA film, 0.001 to
0.002 inches thick. FIG. 48 shows second glass substrate 1012 as it
is adhered to the PSA layer 1010. While a glass protective layer,
which is used as the second glass substrate 1012, has been
described, it will be appreciated that other types of materials may
be used as a protective layer. One example of an alternative
material is epoxy which maybe spun onto the optical layer's surface
after applying the optical layer to the first glass substrate 1002.
One example of a spin-coatable protective layer is a UV cured epoxy
from Master Bond, Inc. (Product Number UV 11-3). The exposed side
of the pressure sensitive adhesive is covered with a protective
film. In operation 820, the wafer sandwich with the retarder film
and the second glass substrate with PSA are placed in an autoclave.
The autoclave is a chamber that is set to an elevated pressure of
30 psi and temperature of 70.degree. C. (without steam). In
operation 822, the wafer is removed from the autoclave after one
hour. The two substrates, in operation 824, are placed on the upper
and lower chucks of a vacuum chamber. The wafer sandwich is placed
on the lower chuck, and aligned to alignment fixtures and the
second glass/PSA layer substrate is placed on the top chuck and
aligned to alignment fixtures as illustrated in FIG. 49. The
protective films are removed from the retarder and the top glass
PSA in operation 826 and the lid is placed on the vacuum chamber in
operation 828. Since there is almost no air in the vacuum chamber,
there is almost no air that will get trapped between the
substrates. In operation 830, the chamber is evacuated to and kept
at 0.050 torr for five minutes. The plunger is pushed down in
operation 832 until the glass/PSA substrate is brought together
with the retarder/sandwich substrate. Alignment rods in the chamber
control the alignment of the two substrates. While maintaining
downward pressure to the plunger, the chamber is vented back to
atmospheric pressure. The resulting sandwich is removed from the
vacuum chamber in operation 834. In operation 836, the resulting
sandwich is placed in the autoclave at 70.degree. C. and 30 psi to
dissolve any small bubbles that may have come from the residual air
in the chamber. The resultant product is shown in FIG. 50. The top
glass (second glass substrate) is cut to a depth of 0.500 mm, or
whatever the thickness of the protective layer is, and directly
above the original glass cuts in operation 838, as illustrated in
FIG. 51. In operation 840, by using a thinner blade 1016 than that
which is used to cut the glass, the retarder/PSA layer is cut to a
depth of 0.800 mm below the surface of the top glass, as shown in
FIG. 52. The blade used here is a 1.6 mil blade made of diamond
particles in a nickel binder and is typically used for cutting soft
materials. As shown in FIG. 53, in operation 842, the silicon wafer
is partially cut from the backside. Again, it is only partially cut
to prevent water from entering the air gap. The individual devices
can then be separated at the cut location as in operation 844 and
are ready to be filled with liquid crystal as in operation 846.
FIG. 54 shows the final product of the singulated integrated
circuit unit 1018 after all cuts have been made.
FIG. 43 is a flow chart describing the alternate embodiment of the
invention in which few steps are eliminated. Instead of having to
prepare the retarder and top glass assembly, the embodiment uses a
prefabricated top glass/PSA/retarder/PSA assembly that can be
attached directly to the wafer sandwich using a similar methodology
to that described above in FIG. 42. The prefabricated assembly as
used in the alternate embodiment is shown in FIG. 55. The only
difference in this procedure is that steps 814, 816, 818 are
eliminated and a new step 815 is added in which we obtain a
retarder film that is already laminated onto a thin piece of glass.
The exposed side of the retarder has a layer of PSA on it that will
allow it to adhere to the cut first glass substrate. FIG. 56
illustrates the cut first glass substrate that is over the silicon
layer.
The sawing process described above is one embodiment of what can be
done In the process described, the first cut glass substrate is
precut on the display sandwich. The protected optical layer(s)
(e.g. retarder) is assembled onto the first glass substrate and the
protective layer of glass is then cut through. The optical layer(s)
are cut using a thinner blade. The back-side of the silicon is
partially cut and the plurality of integrated circuit devices is
singulated to create individual displays.
FIGS. 44A, 44B, and 44C are flow charts which detail three
alternative embodiments of the sawing process. All of the processes
start with an assembled display sandwich. FIG. 44A details method
900 in which the protected retarder is assembled on top of the
display sandwich in operation 920. In operation 930, the protective
layer of glass is cut through. The optical layers are cut through
completely while the first glass substrate 1002 of the display
sandwich is cut through partially using a thinner blade that used
to cut the glass in operation 940. In operation 950, the plurality
of integrated circuit devices are singulated to create individual
displays.
FIG. 44B details method 901 in which the protected optical layer(s)
are assembled on top of the display sandwich in operation 921. In
operation 941, the protective layer is cut through while
simultaneously cutting through the optical layer. The display glass
(first glass substrate) is cut partway through. In operation 951,
the plurality of integrated circuit devices are singulated to
create individual displays.
FIG. 44C details yet another alternate embodiment. In method 902,
the display glass (first glass substrate) is scribed in operation
912. In operation 922, the protected optical layer(s) are assembled
on top of the display sandwich. In operation 932, the protective
layers are cut through. It is possible to also cut through the
optical layer(s) in this operation. If the optical layer(s) are not
cut through in the preceding operation, they can be cut through in
operation 942. The plurality of integrated circuit devices is
singulated to create individual displays in operation 952.
FIG. 57 shows the plurality of integrated circuits with multiple
air gaps created by a spacer layer. The figure illustrates the
wafer scale process as a completed apparatus before the integrated
circuits have been singulated. What is shown is spacer layer 1020
directly attached to semiconductor wafer 1004. Directly above
spacer layer 1020 is first glass substrate 1002. It will be
appreciated that the spacer layer may be arranged relative to each
integrated circuit (IC) so that the contact pads are accessible for
making electrical contacts to the IC. The regions 1022 show the
areas between the IC's which will be sacrificed in the process of
sawing and/or breaking apart the IC's in order to singulate the
IC's. Typically, sawing, from the backside of wafer 1004, will cut
at least partially through the wafer (see FIG. 53) before the IC's
are snapped apart.
FIG. 58 shows an alternative adhesive system 1100 that can be used
in this process. PSA is typically used in the industry, however, an
alternative adhesive system that uses urethane can also be used for
bonding the optical layer(s) to the glass substrates. Operation
1120 details that the urethane is supplied in sheets which can be
laid out over a first substrate (e.g. the display sandwich with or
without a pre-cut as in operation 1110). The second substrate (e.g.
the optical layer(s) which have already been laminated to a
protective glass layer) is aligned to the first substrate display
sandwich in operation 1130 on top of the urethane sheet. The
assembly is placed in a bag in operation 1140 and the extra air is
taken out of the lamination by evacuating to a low vacuum in a
commercial vacuum bag sealing machine. If the assembly is sealed in
a bag, an autoclave can be used in operation 1150 to apply heat and
pressure to ensure that the urethane forms a good bond.
The present invention may be used with displays which are not LCOS
displays, such as passive matrix displays which include a set of
electrodes as a display driver. A display driver drives a display
based upon an electrical input.
In the preceding detailed description, the invention is described
with reference to specific embodiments thereof. It will, however,
be evident that various modifications and changes may be made
thereto without departing from the broader scope of subject matter
as set out in the claim terms. The written and drawing
specification is, accordingly, to be regarded in an illustrative
rather than a restrictive sense.
* * * * *